1. Technical Field
The present invention relates to an apparatus and method for determining physical characteristics of an array of materials as functions of mechanical perturbations and environmental conditions.
2. Discussion
Combinatorial chemistry generally refers to methods and materials for creating collections of diverse materials or compoundsxe2x80x94commonly known as librariesxe2x80x94and to techniques and instruments for evaluating or screening libraries for desirable properties. Combinatorial chemistry has revolutionized the process of drug discovery, and has enabled researchers to rapidly discover and optimize many other useful materials.
Scientists realized that efficient screening techniques were essential for any successful combinatorial research effort. However, since much of the original work in combinatorial chemistry focused on biologically active compounds, early researchers typically employed conventional biological assays as screening methods. Many of these assays were ideally suited for screening combinatorial libraries because they required little or no sample preparation and they could generate useful results using small sample sizes (a mg or less) generally produced in a combinatorial synthesis.
But as researchers began applying combinatorial methods to develop novel non-biological materials, they increasingly found that conventional instruments and methods for characterizing materials were often unsatisfactory for screening. For example, instruments for characterizing physical properties of materialsxe2x80x94viscometers, rheometers, dynamic analyzers, and other mechanical property test instrumentsxe2x80x94are generally unsuitable for screening purposes because they were designed to process one sample at a time. Although the throughput of these serial instruments would likely benefit from automation, many mechanical property test instruments require time-consuming sample preparation, demand more sample than is ordinarily prepared in a high speed research program, and exhibit sluggish environmental control, making such instruments impractical for use as screening tools. Furthermore, the long time scales associated with measuring mechanical properties of polymers, ceramics and other engineered materials often make serial approaches unsuitable as screening methods.
Moreover, competitive pressures are forcing scientists to continually expand their set of screening tools. Many material scientists have embraced combinatorial methodologies because the techniques allow them to develop novel materials in a fraction of the time as conventional discovery methods. This has allowed researchers to tackle a wider range of material design challenges and to consider a broader set of characteristics that ultimately translates into improved material performance. Of course, new design challenges and additional screening criteria mean that laboratories must acquire more screening tools, which if purchased as separate instruments, might offset cost savings associated with combinatorial methods.
Thus, there exists a need for versatile instruments and techniques for screening combinatorial libraries, and especially instruments and methods for measuring physical properties of materials. The present invention, at least in part, satisfies that need.
The present invention provides an apparatus and method for screening combinatorial libraries that addresses many of the problems encountered when using conventional instruments. For example, the disclosed apparatus can measure physical properties of library members in parallel and can perform tests on small amounts of material, which are easily prepared by automated liquid and/or solid handling techniques. Compared to conventional instruments, the disclosed apparatus affords faster sample loading and unloading, for example, through the use of disposable sample arrays and test probes. The present invention is operationally flexible, and permits a single instrument to perform many different material tests through proper selection of sample array format and test probe design. Rapid serial measurements may also be performed.
Thus, one aspect of the present invention provides and apparatus for measuring bulk physical properties of an array of material samples. The apparatus includes a moveable sample holder for containing the array of material samples, and an array of probes for mechanically perturbing the array of material samples. The apparatus also includes an actuator for translating the moveable sample holder and the array of material samples. The actuator moves the array of material samples in a direction normal to a plane defined by the ends of the probes so that the material samples contact the probes. In addition, the apparatus includes a sensor for monitoring the response of the materials to mechanical perturbation by the probes. Typical sensors include force sensors.
A second aspect of the present invention provides a system for screening a combinatorial library of materials by measuring bulk physical properties of the materials. The system includes an array of material samples and probes for mechanically perturbing the samples. Depending on the particular physical property being tested, the array includes materials deposited at predefined regions on flexible or rigid substrates, or materials contained in a group of vessels. The system also includes an actuator for translating the array of material samples in a direction normal to a plane defined by the ends of the probes so the material samples contact the probes. The system also includes a sensor for monitoring the response of the array of material samples to mechanical perturbations by the probes.
A third aspect of the invention provides a method of screening a combinatorial library of materials. The method includes providing an array of material comprising at least five individual samples, and mechanically perturbing the array of materials by contacting at least two of the material samples with probes simultaneously. In addition, the method includes monitoring responses of the samples during the mechanical perturbations. Depending on type of mechanical perturbation, the method can screen libraries of materials based on measurements of many different bulk physical properties. For example, the inventive method can measure physical properties related to Young""s modulusxe2x80x94including flexure, uniaxial extension, biaxial compression, and shear. In addition, the method can measure physical properties related to hardness (indentation), failure (stress and strain at failure, toughness), adhesion (tack, loop tack), and flow (viscosity, melt flow indexing, and rheology), among others.